1. Technical Field
The present invention relates to an object sensing device, which radiates a laser beam and the like forward as an exploring wave and senses a reflected wave of the laser beam to sense an object positioned ahead.
2. Related Art
In some conventional radar devices mounted to a vehicle, exploring waves, such as a laser beam and a radio wave, are radiated in front of an own vehicle, a reflected wave of the exploring wave is sensed to sense objects, such as a car ahead, which are positioned in front of the own vehicle, and a distance to the sensed object is measured. A sensing result of the radar device can be applied to vehicle running control, such as Adaptive Cruise Control (ACC) in which the distance to the car ahead is kept constant and Low Speed Following (LSF) during backup (during a low speed). The radar device can also be applied to a pre-crush safety system that brakes the own vehicle to reduce a damage at the time of a collision when sensing the car ahead or a stopped object, which is positioned in front of the own vehicle and hardly avoids the collision with the own vehicle.
In some radar devices, a raindrop sensing function of determining a rainfall state, which can be used in automatic control of a wiper of the vehicle, is integrally configured (for example, see Japanese Unexamined Patent Publication No. 10-329653). The radar device of Japanese Unexamined Patent Publication No. 10-329653 includes a light receiving element (stain sensing PD) and a light receiving element (ranging PD). The stain sensing PD receives light randomly reflected from a light projecting/light receiving surface (a transmission window made of glass or synthetic resin) through which a laser beam radiated forward is transmitted. The ranging PD receives light, which is transmitted through the light projecting/light receiving surface and reflected by the object positioned forward. In each predetermined period (for example, ten minutes), the radar device of Japanese Unexamined Patent Publication No. 10-329653 repeats processing of sensing a situation in which the raindrop adheres to the light projecting/light receiving surface, namely, rainfall amount to sense the rainfall state based on a change in light receiving amount of the stain sensing PD. The radar device of Japanese Unexamined Patent Publication No. 10-329653 also senses the object positioned forward and the distance to the object by receiving the reflected light using the ranging PD.